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# coding=utf-8 | |
# Copyright 2022 The IDEA Authors. All rights reserved. | |
# | |
# Licensed under the Apache License, Version 2.0 (the "License"); | |
# you may not use this file except in compliance with the License. | |
# You may obtain a copy of the License at | |
# | |
# http://www.apache.org/licenses/LICENSE-2.0 | |
# | |
# Unless required by applicable law or agreed to in writing, software | |
# distributed under the License is distributed on an "AS IS" BASIS, | |
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
# See the License for the specific language governing permissions and | |
# limitations under the License. | |
# ------------------------------------------------------------------------------------------------ | |
# Modified from: | |
# https://github.com/facebookresearch/ConvNeXt/blob/main/models/convnext.py | |
# ------------------------------------------------------------------------------------------------ | |
import torch | |
import torch.nn as nn | |
import torch.nn.functional as F | |
class LayerNorm(nn.Module): | |
r"""LayerNorm which supports both channel_last (default) and channel_first data format. | |
The inputs data format should be as follows: | |
- channel_last: (bs, h, w, channels) | |
- channel_first: (bs, channels, h, w) | |
Args: | |
normalized_shape (tuple): The size of the input feature dim. | |
eps (float): A value added to the denominator for | |
numerical stability. Default: True. | |
channel_last (bool): Set True for `channel_last` input data | |
format. Default: True. | |
""" | |
def __init__(self, normalized_shape, eps=1e-6, channel_last=True): | |
super().__init__() | |
self.weight = nn.Parameter(torch.ones(normalized_shape)) | |
self.bias = nn.Parameter(torch.zeros(normalized_shape)) | |
self.eps = eps | |
self.channel_last = channel_last | |
self.normalized_shape = (normalized_shape,) | |
def forward(self, x): | |
"""Forward function for `LayerNorm`""" | |
if self.channel_last: | |
return F.layer_norm(x, self.normalized_shape, self.weight, self.bias, self.eps) | |
else: | |
u = x.mean(1, keepdim=True) | |
s = (x - u).pow(2).mean(1, keepdim=True) | |
x = (x - u) / torch.sqrt(s + self.eps) | |
x = self.weight[:, None, None] * x + self.bias[:, None, None] | |
return x | |